7. A heat engine takes in heat at 1000 K and expels it at 300K. a. What is its e

Question

7. A heat engine takes in heat at 1000 K and expels it at 300K.

a. What is its efficiency?

b. If it takes in 1000 joules, how much work is done?

8. It takes 1150 watts for a 68kg person to run at 15 km/h.

It takes 380 watts for a 68kg person to walk 5 km/h.

a. How much energy does it takes to run 15 km.?

b. How much energy does it takes to walk 15 km.?

9. An Ice skater has a moment of inertia I = 5kg*m2 and is rotating

twice a second.

a. What is her kinetic energy?

b. What is her angular momentum?

Explanation / Answer

Efficiency of the heat engine is

n =1-T2/T1 =1-300/1000=0.70 Or 70%

If it takes 1000Joules of energy the efficiency n =Workdone by heat engine/Heat taken

From first part efficiency n=0.7, and Q =1000J then work done is W =n*heat taken =0.7*1000=700J

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